Electroplating of copper



United Statesw Patent 3,373,095 ELECTROPLATING OF COPPER Charles N. Abbott, Dayton, Ohio, assignor to The Dayton Bright Copper Company, Dayton, Ohio N 0 Drawing. Continuation-impart of application Ser. No.

375,344, June 15, 1964. This application June 5, 1967,

Ser. No. 643,405

8 Claims. (Cl. 20452) ABSTRACT OF THE DISCLOSURE The present invention relates to improved extender compositions used in copper electroplating comprising a sulfurized sulfonated aromatic compound, an amino derivative of a triarylmethane, and as a leveling agent a compound containing the radical i e The combination of the ingredients of the type specified gives synergistic results in the form of improved brightness and leveling properties over a wider range of current density than previous compositions used in copper electroplating baths.

This is a continuation-in-part of my United States Serial No. 375,344 filed June 15, 1964, now abandoned.

FIELD OF THE INVENTION My invention relates to the electroplating of copper on metal bases from acidic electrolyte solutions, and to compositions for use therein. More particularly, it relates to the production of copper plated objects of improved physical characteristics by the incorporation in the electrolyte of addition agents containing the radical where X is S or N, and particularly, in combination with sulfurized sulfonated aromatic or hydroaromatic compounds, and substitution products thereof, and amino derivatives of a triarylmethane, and to compositions containing such materials.

PRIOR ART The plating of base metals with copper prior to plating/with other metals has frequently been found advisable or necessary in order to obtain metal finishes of particular characteristics. In order, however, to obtain satisfactory coatings of the final metal it is essential to have on the base metal an initial plate or coating of copper of suitable characteristics. It is, for example, highly important that the copper plate adhere well to the base metal, and that a smooth, bright uniform surface be obtained, and also that the copper plate possess suitable ductility. A rough surface, or one produced under plating conditions which produce burning or treeing will not usually give a satisfactory secondary plate.

It has been found that when copper plating from an acidic electrolyte, the incorporation in the electrolyte bath of certain addition agents greatly improves the characteristics of the copper plate and makes the latter more suitable for secondary plating with other metals. Various types of such addition agents have been used for the purpose of giving smooth, bright or semibright deposits of copper. Examples of such addition agents pre- 3,373,695 Patented Mar. 12, 1968 viously used include, urea, thiourea and derivatives thereof, casein, sugar, glue and other materials of similar character. While these and many of the other additives previously tried have been found to give some of the desired characteristics to the copper plate, such as, for example, brightness or semi-brightness, the resulting deposits have generally been found to be subject to various defects such as brittleness, lack of uniformity, etc. Also, the plating operations using such addition agents have been difficult to carry out without incurring detrimental effects such as burning or treeing, and closer regulation of the plating temperature and other operating conditions such as current density have been necessary in order to obtain satisfactory results. In addition, the percentage of rejects is frequently high, thus increasing the cost of operation.

Attempts have also been made in the past to use mixtures of additives in order to neutralize or overcome the defects resulting from the use of single additives. Such attempts, however, have not been very successful since the use of such mixtures has usually magnified instead of reduced both operating problems and the defects in the resulting copper plates.

SUMMARY AND OBJECTS Applicant has discovered a neW type of additive composition for copper plating operations consisting of a mixture of agents which gives copper deposits of improved properties and which at the same time is relatively free from most of the previous plating difliculties. The incorporation in this mixed additive of a new type of leveling agent has given especially good leveling characteristics, with the result that much less buffing is required than has been necessary with previously known types of additives and leveling agents. This is of particular importance in reducing the cost of preparing plates for secondary plating. The copper plates obtained with my new additive composition have excellent brightness and ductility, thus improving their suitability for secondary plating. Of equal if not greater importance is the fact that the use of my new additive composition permits the plating operation to be satisfactorily carried out over a wider operating range than is possible with previous additives, thus reducing the percentage of rejects as well as over-all operating costs.

DESCRIPTION My new additive composition for use in copper electroplating electrolytes essentially comprises a mixture of sulfurized sulfonated aromatic or hydroaromatic hydrocarbons, and substitution products thereof; amino derivatives of a triarylmethane; and compounds containing the radical 3 used in his claimed combination, these compounds serve their function as brighteners in an effective manner and without the operating difliculties incurred when the materials are used alone. Also, much less of the material is required when used in my claimed combination.

A wide range of sulfurized sulfonated aromatic and hydroaromatic hydrocarbons, and substitution products thereof, can be satisfactorfly used in my new additive compositions, when soluble to the specified degree in the plating solution. Examples of suitable compounds of this type include sulfurized sulfonated benzene, sulfurized sulfonated toluene, sulfurized sulfonated xylene, sulfurized sulfonated naphthalene, sulfurized sulfonated anthracene, sulfurized sulfonated phenanthrene, sulfurized sulfonated diphenyl, and hydrogenated derivatives of the same. These materials comprise the colloidal sulfonated reaction products of an aromatic or hydroaromatic hydrocarbon, or substitution product thereof, with a sulfurizing agent such as, for example, sulfur chloride, sulfuryl chloride or thionyl chloride. The sulfurized aromatic or hydroaromatic or hydroaromatic hydrocarbon, or substitution derivative thereof, may be sulfonated by conventional means, as by fuming sulfuric acid. Or, the sulfonation may first be effected and followed by sulfurization. The product in either case is water soluble or water dispersible. Sulfurized sulfonated benzene suitable for use in the present invention may, for example, be

produced by sulfonating 112 g. of benzene with 350 g. of 30% oleum by conventional means and then sulfurizing the resulting mixture with 3 g. of sulfur monochloride by conventional means.

The amino derivatives of triarylmethane are dyestuffs soluble in the plating solutions to the specified amounts. Suitable amino derivatives of this type include dyestuffs commonly known as Guinea Green B, Brilliant Milling Green B, Patent Blue V, Light Green SFA, Neptune Blue, Erioglycine or Alphazurine F. G., Chromoxane Brilliant Violet 5R, Soluble Blue, Methyl Blue or Helvetia Blue, Brilliant Indocyanine 6B, Acid Violet 6B, and Wool Fast Blue FBL. The structural formula of these dyes are shown in United States patent application Ser. No. 279,006 filed May 8, 1963, now abandoned.

The addition agents, serving primarily as leveling agents, used in my addition compositions are compounds wherein X is selected from and where A is The following are examples of typical compounds of the above types which have given excellent results as leveling agents in my new additive compositions for copper plating:

(1) '5-Chloromercurithio-2,3-diphenyl 2H tetrazolium chloride C5H5N-N os1IgCl or (2) 2-Thiazolidinethionomercuric chloride H2CN GSHg01 HzCS (3) Bis (Z-thiazolidinethiono) mercury (4) Thiocarbohydrazido mercuric chloride (7) Bis (1-acety1-2-hydrantointhiono) mercury 8) Z-Imidazolidinethionomercuric chloride Bic-N (l) Z-Benzimidazolethionomercuric chloride H it CsHgo1 N.

(11) Bis (2-benzimidazolethiono) mercury H H i: i;

(12) Bis (2-benzothiazolethiono) mercury (13) Bis (1-phenyl-2-tetrazole-5-thiono) mercury H CH (16) Diphenylthiocarbazonomercuric chloride (17) Bis (diphenylthiocarbazono) mercury The compounds of the above type containing the radical can be produced by reacting the basic sulfur-containing compound with mercuric chloride in a suitable solvent. The desired product can then be recovered by filtration followed by crystallization or recrystallization. For example, chlorornercurithio-2,3 -diphenyl-2H-tetrazolium chloride can be prepared by adding a mixture of mercuric chloride to a suspension of diphenylthiocarbazone in benzene, using a molar ratio respectively of 1:2. After refluxing this mixture for a number of hours a reaction product is obtained from which the desired product can be produced by washing with a suitable solvent such as chloroform, benzene, Xylene, chlorobenzene, carbontetrachloride, acetone, ethyl acetate, or other suitable solvent for removal of the undesired compounds of the reaction. Other suitable procedures and solvents may also be used, as the preferred procedure will vary with the properties of the sulfur-containing base used.

My new leveling agents of the above types can be used in plating compositions with satisfactory results in concentrations ranging from 0.0005 to 0.1 gm./1., although I prefer to use concentrations ranging from 0.001 to 0.04 gm./l. When used in combination with the other additives described herein, the sulfurized sulfonated aromatic and hydroaromatic hydrocarbons are used in amounts ranging from 0.0015 to 0.5 gm./l., and preferably within the range of 0.01 to 0.04 gm./l. The concentration of the particular dye used can vary between 0.001 to 2.0 gm./l. with a preferred range of 0.015 to 0.5 gm./l.

I have found that when using combination additives of the above type smaller quantities of additives are required to give copper plates having physical properties of materially improved physical characteristics over those obtainable with previously known additives or combinations of additives for copper plating. I have found that not only can copper plated surfaces of greatly improved physical characteristics be obtained by the use of my new additive compositions but that improved results can be obtained over a wider range of operating conditions, and with smaller amounts of additives than previously possible. I obtain improved results by adding to a copper electrolyte of the conventional type from 0.001-0.1 gm./l. of the above specified leveling agents and the specified amounts of one or more of the additional additives hereinabove described. Using such additive compositions and a current density ranging from 5 amperes/sq. ft. to 300 am peres/sq. ft., and even somewhat higher, but preferably within the ranges of 20 amperes/sq. ft. to 200 amperes/ sq. ft., and with the electrolyte at a temperature of from 20 to 40 C., but preferably Within the range of 24 to 30 C., I have produced semi-bright to bright deposits of copper on base metals which were suitable for nickel plating without the necessity of buffing or polishing or otherwise pre-treating the copper plate prior to nickel plating. The use of the above-designated leveling agents in the plating composition is particularly effective in producing copper plates of improved leveling characteristics, with the result that the subsequently plated deposits were more nearly perfect. The copper deposits were quite resistant to corrosion, yet ductile and easily buffed in the relatively few cases where this was necessary or desirable. A fine grain deposit of copper was normally obtained over a wide range of current density without the hazard of burning and tree formation. An additional advantage in the use of my new additive compositionsis that the improved results described above are obtainable with the aid of materially reduced quantities of the additive composition, thus effecting improved results at a reduced cost, as well as fewer breakdownproducts in .the bath resulting in fewer purifications.

Electroplating tests were carried out with my new additive compositions in a 300 ml. Hull cell with air agitation at temperatures ranging from 20 to 40 C., using amounts of the additives specified above, and for comparison purposes equivalent amounts of additives customarily used in the industry. It was uniformly found that my new additive compositions not only permitted the use of smaller amounts'of additive compositions but, in addition, these reduced amounts gave copper plates of smaller grain structure, of increased corrosion resistance, and increased ductility. The plates were also more uniform in appearance, and more level, of improved brightness and substantially free from burning and tree formation and other irregularities, even when plated at high current densities.

7 Satisfactory results were obtained with current densities ranging from to 300 amperes/sq. ft., and even above.

It has been found that the addition of my new additive compositions to an acid copper electrolyte of the type customarily used in the industry permitted a increase in current density without encountering the usual 'burnin g or treeing effect at the edges of the workpiece. At the same time, the overall bright plating range was increased and the deposits of the copper were of a more even, uniform lustre than when using conventional copper plating electrolytes containing conventional additives. It was further observed that finished chrome plated products, e.g., plated 20 minutes in an acid copper electrolyte bath, followed by 12 minutes in a nickel sulfate bath and then chrome plated, were far superior in color and appearance and more level than a similar plate obtained using the same process cycle and a conventional type additive.

The following specific examples are illustrative but not limitative of my invention, it being understood that similar improved results are obtainable with other combinations of the different ingredients of my new additive composition specified above. All such variations which do not depart from the basic concept of the invention and composition disclosed above are intended to come within the Light Green SFA dye 0.03

A steel panel plated for one-half hour at 80 F. at a current density of 60 amperes/ sq. ft. gave a plate of excellent brightness and ductility and of excellent leveling.

Example 2 In this experiment carried out as described in Example 1, the electrolyte had the following composition:

Gm./l. Copper sulfate 225 Sulfuric acid w 60 Acid fast Violet dye 0.05 Sulfurized sulfonated benzene 0.05 2-thiazolidine thionomercuric chloride 0.025

The plating results were similar to those of Example 1.

Example 3 Gm./l. Copper sulfate 22S Sulfuric acid 60 Sulfurized sulfonated xylene 0.05 Bis (thiocarbohydrazido) mercury 0.01 Patent Blue V dye 0.04

The plating results were similar to those of Example 1.

Example 4 In this experiment, carried out as described in Example I, the following electrolyte composition was used:

Gm./l. Copper sulfate 225 Sulfuric acid 60 Sulfurized sulfonated naphthalene 0.03 1-acetyl-2 hydrantointhionomercuric chloride 0.02 Neptune Blue dye 0.03

The plating results were similar to those of Example 1.

The plating results were similar to those of Example 1.

Example 6 In this experiment, carried out as described in Example 1, the following electrolyte composition was used:

Gm./l. Copper sulfate 2.25 Sulfuric acid 60 Sulfurized sulfonated diphenyl 0.03 1-methyl-2-imidazolethionomercuric chloride 0.001 Chromoxane Brilliant Violet 5R 0.02

The plating results were similar to those of Example 1.

Example 7 In this experiment, carried out as described in Example 1, the electrolyte used had the following composition:

G1m./l. Copper sulfate 225 Sulfuric acid 60 Sulfurized sulfonated benzene 0.05 Methyl Blue 0.02 Bis (diphenylthiocarbazono) mercury 0.006

The plating results were similar to those of Example 1.

Example 8 In this experiment carried out as described in Example 1, the following electrolyte was used:

Gm./l. Copper sulfate 225 Sulfuric acid 60 Patent Blue V 0.15 Bis (1-phenyl-2-tetrazole-5-thiono) mercury 0.05

The plating results were not as good as those obtained in Example 1, the deposit being only semi-bright with poor leveling.

Example 9 In this experiment, carried out as described in Example l, the following electrolyte was used:

Gm./l. Copper sulfate 225 Sulfuric acid 60 Bis (thiocarbohydrazido) mercury 0.01

The overall plating results were unsatisfactory both as to brightness and leveling.

In order to obtain satisfactory plating results, it has been found to be necessary to use all three of the constituents of my new additive composition set forth above. When using only the sulfurized sulfonated aromatic compound and a dye, a low level of brightness and a narrow brightness range in relation to current density, with very poor leveling, is obtained. When using only a dye and the new leveling agents of the present application, only semi-bright deposits with very little leveling and only in low current areas are obtained. When using only a sulfurized sulfonated aromatic compound and a leveling agent of the type disclosed herein, substantially the same results were obtained as when using only a sulfurized sulfonated aromatic compound and a dye, that is, only semibright deposits with little or no leveling were obtained. While it may be found desirable to vary the amounts of the three constituents within the ranges specified above in order to obtain particular desired results, it is only when all three constituents are used that the most desirable results are obtained. From this it will be noted that the results obtained from the use of my three constituents are in no sense additive but in fact of a synergistic character.

While the invention has been described and specific examples ot the electroplating baths and conditions for obtaining the improved plating results aforementioned set forth, it will be understood that changes and substitutions can be made by those skilled in the art without departing from the invention. For example, acid copper compositions of ditferent concentrations can be employed and other additives can also be incorporated into the compositions. Also, any of the various ingredients shown in the specific examples can be substituted by the specified amounts of any of the other specified additives so long as they are soluble in the electrolyte to the specified extent. The appended claims thus are intended to cover all such equivalents and methods of use as come within the true spirit and scope of the foregoing disclosure.

What is claimed is:

1. Ari electrolyte for electroplating copper consisting essentially of an aqueous acid solution of copper sulfate and free sulfuric acid and having dissolved therein an additive composition comprising a sulfurized sulfonated aromatic or hydroarornatic hydrocarbon or substitution product thereof, an amino derivative of triarylmethane and a compound containing the radical wherein X is selected from said additive composition being used in an amount sufiicient to give a bright, level deposit.

2. The electrolyte of claim 1 wherein the sulfurized sulfonated aromatic compound is selected from the group consisting of sulfurized sult'onated benzene, sulfurized sulfonated toluene, sulfurized sulfonated xylene, sulfurized sulfonated naphthalene, sulfurized sulfonated anthracene, sulfurized sulfonated phenanthrene, sulfurized sultonated diphenyl, and hydrogenated derivatives of same.

3. The electrolyte of claim 1 wherein the amino derivative of triarylmethane is selected from the group consisting of Guinea Green B, Brilliant Milling Green B, Patent Blue V, Light Green SFA, Neptune Blue, Erioglycine or Alphazurine F. G., Chromoxane Brilliant Violet 5R, Soluble Blue, Methyl Blue or Helvetia Blue, Brilliant Indocyanine 6B, Acid Violet 6B, and Wool Fast Blue FBL.

4. The electrolyte of claim 1 wherein the compound containing the radical i is selected from the group consisting of 5-chloromercurithio-2,3-diphenyl-2H-tctrazolium chloride; Z-thiazolidinethionomercuric chloride; bis (Z-thiazolidinethiono) mercury; thiocarbohydrazido mercuric chloride; bis (thiocarbohydrazido) mercury; 1-acetyl-2-hydrantointhionomercuric chloride; his (1-acetyl-2-hydrantointhiono) mercury; 2-imidazolidinethionomercuric chloride; bis (Z-imidazolidinethiono) mercury; 2-benzimidazolethionomercuric chloride; bis (2-benzimidaz0lethiono) mercury; bis (2-benzothiazolethiono)) mercury; bis (l-phenyl-Z- tetrazole-S-thiono) mercury; bis (l-methyl-Z-imidazolethiono) mercury; 1-methyl-2-imidazolethionomercuric chloride; diphenylthiocarbazonomercuric chloride; and his (diphenylthiocarbazono) mercury.

5. The method of electroplating copper comprising the step of electrodepositing copper from an aqueous acidic copper plating bath containing dissolved therein an additive composition comprising about 0.0015 to 0.5 gm./l. of a sulfurized sulfonated aromatic or hydroaromatic hydrocarbon or substitution product thereof, about 0.0015 to 1.0 gm./l. of an amino derivative of triarylmethane, and about 0.005 to 0.1 gin/1. of a compound containing the radical wherein X is selected from said additive composition serving to efiect the deposition of the copper in a bright, level form.

6. The method of claim 5 wherein the sulfurized sulfonated aromatic hydrocarbon compound is selected from the group consisting of sulfurized sulfonated benzene, sulfurized sulfonated toluene, sulfurized sulfonated Xylene, sulfurized sulfonated naphthalene, sulturized sulfonated anthracene, sulfurized sult'onated phenanthrene, sulfurized sulfonated diphenyl, and hydrogenated derivatives of same.

7. The method of claim 5 wherein the amino derivative of triarylmethane is selected from the group consisting of Guinea Green B, Brilliant Milling Green B, Patent Blue V, Light Green SFA, Neptune Blue, En'oglycine or Alphazurine F. G., Chromoxane Brilliant Violet 5R, Soluble Blue, Methyl Blue or Helvetia Blue, Brilliant Indocyanine 6B, Acid Violet 6B, and Wool Fast Blue FBL.

8. The method of claim 5 wherein the compound containing the radical at I is selected from the group consisting of S-chlorornercurithio-2,3-diphenyl-2P-tetrazolium chloride; 2-thiazolidinethionomercuric chloride; bis (Z-thiazolidinethiono) mercury; thiocarbohydrazido mercuric chloride; bis (thiocarbohydrazido) mercury; 1-acetyl-2hydrantointhionomercuric chloride; bis (l-acetyl-Z-hydrantointhiono) mercury; 2-imidazolidinethionomercuric chlo ride; bis (Z-imidazolidinethiono) mercury; 2-benzirnidazolethionomercuric chloride; bis (Z-benzirnidazolethiono) mercury; bis (Z-benzothiazolethiono) mercury; bis (1-phenyl-2-tetrazole-5-thiono) mercury; bis (1-methyl-2- imidazolethiono) mercury; l-rnethyl-2-imidazolethionomercuric chloride; diphenylth-iocarbazonomercuric chloride; and his (diphenylthiocarbazono) mercury.

References Cited UNITED STATES PATENTS 2,424,887 7/1947 Henricks 20452 2,805,194 9/1957 Beaver et a1. 20452 2,931,760 4/1960 Westbrook 20452 3,081,240 3/1963 Strauss et al 20452 3,252,987 5/1966 Hart 20452 3,267,010 8/1966 Creutz 20452 HOWARD S. WILLIAMS, Primary Examiner.

JOHN H. MACK, Examiner.

G. KAPLAN, Assistant Examiner. 

